How to convert an HDR Image created / rendered on Blender to a format acceptable on social media and websites?
Sorry for the links only answer, but this is too long for comments.

You are mixing two different concepts:
1. HDRi
stands for High Dynamic Range image, that has larger colour values than those that can be displayed by any screen. They are used mostly as environment textures to light scenes.
2. 360 images
concept of environment projection https://wiki.panotools.org/Projections
Watch https://www.coursera.org/lecture/360-vr-video-production/equirectangular-projection-cubemaps-uTv8r
Most HDRi is mapped used in 3D and VR is using equirectangular projection, but is not mandatory.
As to how to do this in blender, it has been asked before:
Blender panoramic render
Is it possible to render a panorama in perspectives other than full 360&#176;x180&#176;?
equirectangular rendering for Blender Internal?
how do I bake an animated sky box using cycles?